Electrically heated diesel particulate filter (dpf)

ABSTRACT

A diesel particulate filter assembly includes a diesel particulate filter (DPF) and an electric heater that is integrally formed at an upstream end of the DPF. The electric heater includes a heating substrate and a resistive heating element. The heating substrate includes a central region and a boundary region around the central region. The resistive heating element includes a plurality of conductive portions. Adjacent ones of the conductive portions in the central region form a first spacing. Adjacent ones of the conductive portions in the boundary region form a second spacing. The second spacing is smaller than the first spacing.

STATEMENT OF GOVERNMENT RIGHTS

This invention was produced pursuant to U.S. Government Contract No. DE-FC-04-03 AL67635 with the Department of Energy (DOE). The U.S. Government has certain rights in this invention.

FIELD

The present disclosure relates to diesel engines, and more particularly to diesel particulate filter (DPF) regeneration.

BACKGROUND

The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent that it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

A combustion cycle of a diesel engine produces particulates that are typically filtered from the exhaust gases. A diesel particulate filter (DPF) may be disposed along the exhaust stream to filter the diesel particulates from the exhaust. As the carbon particulates accumulate in the filter, flow resistance for the exhaust gas increases. The DPF becomes full and must be regenerated to remove the trapped diesel particulates. During regeneration, the diesel particulates are burned within the DPF to enable the DPF to continue its filtering function.

Regeneration may involve injecting fuel into the exhaust stream after the main combustion event. The post-combustion injected fuel is combusted over catalysts in the exhaust stream. The heat released during the fuel combustion on the catalysts heats the exhaust gas to burn the trapped soot particulates in the DPF. This approach, however, can result in high temperature excursions in the exhaust system.

SUMMARY OF THE INVENTION

Accordingly, a diesel particulate filter assembly includes a diesel particulate filter (DPF) and an electric heater that is integrally formed at an upstream end of the DPF. The electric heater includes a heating substrate and a resistive heating element. The heating substrate includes a central region and a boundary region around the central region. The resistive heating element includes a plurality of conductive portions. Adjacent ones of the conductive portions in the central region form a first spacing. Adjacent ones of the conductive portions in the boundary region form a second spacing.

In one feature, the second spacing is smaller than the first spacing. In another feature, the conductive portions in the boundary region have a resistance per unit length larger than that in the central region.

Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a schematic view of an exemplary diesel engine system that includes a diesel particular filter (DPF) assembly according to the present disclosure;

FIG. 2 is a schematic cross-sectional view of a DPF assembly including an electric heater according to the present disclosure; and

FIG. 3 is a plan view of an electric heater of the DPF assembly according to the present disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the term module refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, or other suitable components that provide the described functionality.

A diesel particulate filter (DPF) assembly may include an electric heater integrated with a DPF. The electric heater includes a heating substrate and a resistive heating element that includes a plurality of conductive portions. Adjacent conductive portions in a central region of the heating substrate form a first spacing. Adjacent conductive portions in a boundary region of the heating substrate form a second spacing that is smaller than the first spacing. As such, the conductive portions in the boundary region generate more heat per unit area of the heating substrate to compensate for insufficient radiant heat in the boundary region.

Referring now to FIG. 1, an exemplary diesel engine system 10 is schematically illustrated in accordance with the present disclosure. It is appreciated that the diesel engine system 10 is merely exemplary in nature and that the diesel particulate filter (DPF) regeneration system described herein can be implemented in various diesel engine systems implementing a DPF. The diesel engine system 10 includes a diesel engine 12, an intake manifold 14, a common rail fuel injection system 16 and an exhaust system 18. The exemplary engine 12 includes six cylinders 20 configured in adjacent cylinder banks 22, 24 in V-type layout. Although FIG. 1 depicts six cylinders (N=6), it can be appreciated that the engine 12 may include additional or fewer cylinders 20. For example, engines having 2, 4, 5, 8, 10, 12 and 16 cylinders are contemplated. It is also anticipated that the DPF of the present disclosure can be implemented in an inline-type cylinder configuration, as discussed in further detail below.

Air is drawn into the intake manifold 14 through a throttle (not shown). Air is drawn into the cylinders 20 from the intake manifold 14 and is compressed therein. Fuel is injected into the cylinder 20 by the common rail injection system 16 and the heat of the compressed air ignites the air/fuel mixture. The exhaust gases are exhausted from the cylinders 20 and into the exhaust system 18. The diesel engine system 10 may include a turbocharger 26 that pumps additional air into the cylinders 20 for combustion with the fuel and air drawn in from the intake manifold 14.

The exhaust system 18 includes exhaust manifolds 28, 30, exhaust conduits 32, 34, a catalyst 36, a diesel particulate filter (DPF) assembly that includes a diesel particulate filter (DPF) 38 and an electric heater 40. First and second exhaust segments are defined by the first and second cylinder banks 22, 24. The exhaust manifolds 28, 30 direct the exhaust segments from the corresponding cylinder banks 22, 24 into the exhaust conduits 32, 34. The exhaust is directed into the turbocharger 26 to drive the turbocharger 26. A combined exhaust stream flows from the turbocharger 26 through the catalyst 36 and the heater 40 to the DPF 38. The DPF 38 filters particulates from the combined exhaust stream before the exhaust stream is released to atmosphere. The electric heater 40 may be integrated in the DPF 38 and may selectively heat the exhaust stream flowing through the electric heater 40 to regenerate the DPF 38, as explained in further detail below.

A control module 42 regulates operation of the diesel engine system 10 and communicates with an intake manifold absolute pressure (MAP) sensor 44 and an engine speed sensor 46. The MAP sensor 44 generates a signal indicating the air pressure within the intake manifold 14 and the engine speed sensor 46 generates a signal indicating engine speed (RPM). The control module 42 determines an engine load based on the RPM and fueling rates. The fueling rate is generally measured in fuel volume per combustion event. Engine output is controlled via the fueling rate.

The electric heater 40 may be connected to a power source 48 through electrical terminals (not shown). When operating in a regeneration mode, electric current selectively flows across the electric heater 40 so that the electric heater 40 can generate heat.

Referring to FIG. 2, the DPF 38 may include a monolith particulate trap and includes side walls 49 that define alternating inlet channels 50 and outlet channels 52. The side walls 49 of the DPF 38 may include ceramic honeycomb walls of chordierite material. Exhaust gases such as those generated by the engine 12 flow through the inlet channels 50 and the side walls 49 and exit through the outlet channels 52. Soot particulates 56 are deposited on the side walls 49 as the exhaust gas flows from the inlet channels 50 to the outlet channels 52. It is appreciated that any ceramic honeycomb material is considered within the scope of the present invention.

The electric heater 40 may be integrally mounted to an end wall 60 of an upstream end 62 of the DPF 38 and may define a plurality of channels 64 to allow the exhaust gas and the soot particulates 56 to pass through. Suitable materials for the heating substrate 70 include, but are not limited to, cordierite and silicon carbide.

During the regeneration process, the electric heater 40 generates heat to heat the soot particulates 56 that flow through the channels 64. For example, the control module 42 may activate the power source 48 to provide electric current to the electric heater 40. Sufficient heat is transferred from the electric heater 40 to the soot particulates 56 to induce exothermic combustion thereof, releasing additional heat. The heat then flows into the DPF 38 to heat the soot particulates 56 therein. As a result, a cascading effect is achieved through the DPF 38. Heat generated through combustion of upstream soot particulates 56 induces combustion of downstream soot particulates 56. In other words, the electric heater 40 functions as an ignition catalyst that ignites or lights off the upstream soot particulates 56, and the combustion heat of the particulates in turn ignites the downstream soot particulates 56. In this manner, all of the soot particulates 56 within the DPF 38 are combusted to regenerate the DPF 38.

Referring to FIG. 3, the electric heater 40 may include a heating substrate 70 and an annular mounting portion 72 that surrounds the heating substrate 70. The annular mounting portion 72 includes a plurality of holes 74. The electric heater 40 may be bolted to the wall 62 of the DPF 38 through the holes 74.

The heating substrate 70 includes a central region 76 and a boundary region 78 that surrounds the central region 76. The size/diameter of the central region 76 as shown is merely exemplary and may be increased or decreased. A resistive heating element 80 is formed on a surface of, or embedded in, the heating substrate 70. The resistive heating element 80 may include, for example only, a resistive wire or a resistive film. The resistive wire/film may have a constant diameter/width to have a constant resistance per unit length along the length of the resistive heating element 80. Therefore, the resistive heating element 80 generates a constant heat along the length of the resistive heating element 80. The resistive heating element 80 may be made of, for example, INVAR42® (nickel-iron alloy), stainless steel, nichrome® (nickel-chromium alloy), or any other high temperature alloy.

The resistive heating element 80 is arranged to form a continuous spiral-like pattern and includes a plurality of conductive portions 82, 84, 86, 88, 90 and 92. The plurality of conductive portions 82, 84, 86, 88, 90 and 92 may have a ring-like configuration and are connected in series to form a single unit. The plurality of conductive portions 82, 84, 86, 88, 90, and 92 define a spacing s₁, s₂, s₃, s₄ and s₅ with an adjacent conductive portion. The spacing between adjacent conductive portions may vary and may have a relationship of, for example only, s₁>s₂>s₃>s₄>s₅ as shown in FIG. 3. Alternatively, the spacing may have a relationship of, for example only, s₁>s₂=s₃=s₄>s₅, s₁=s₂=s₃=s₄>s₅, or s₁>s₂=s₃=s₄=s₅. In any case, the largest spacing s1 is present in the central region 76 and between the conductive portions 82 and 84. The smallest spacing s₅ is present in the boundary region 78 and between the conductive portions 90 and 92. Due to a smaller spacing in the boundary region 78, the radiant heat from the adjacent conductive portions in the boundary region 78 may be increased.

Generally, total thermal output in a region of the heating substrate 70 includes heat generated by the conductive portion located in the region and radiation heat from an adjacent conductive portion outside the region. Radiant energy per unit area emitted by a point source of radiation decreases as the square of the distance from the source to the point of detection.

When the conductive portions of the resistive heating element are arranged to have equal spacing, the surface temperature of the heating substrate 70 in the boundary region 78 is generally lower than that in the central region 76 due to insufficient radiant heat from adjacent conductive portions. The boundary region 78 receives radiant heat from only one direction (i.e., from the center), whereas the central region 76 receives radiant heat from multiple directions (i.e., radially from the conductive portions that surround the central region 76).

By forming a smaller spacing in the boundary region 78, the radiation heat per unit area in the boundary region 78 may be increased. The surface temperature of the boundary region 78 may be increased to be equal to or higher than that of the central region 76. Therefore, the trapped soot particulates in the boundary region may be effectively burned during regeneration.

Alternatively, the conductive portions 82, 84, 86, 88, 90, 92 of the resistive heating element 80 may be arranged to have a constant spacing, i.e., s₁=s₂=s₃=s₄=s₅. In this instance, the resistive heating element 80 may have a varied resistance per unit length along the length of the resistive heating element 80 to generate varied heat along the length of the resistive heating element 80. The varied resistance may be achieved, for example only, by changing the diameter/width of the resistive wire/film along its length. To achieve a more uniform surface temperature throughout the heating substrate or a higher surface temperature in the boundary region 78, the conductive portion 92 in the boundary region 78 may have a higher resistance per unit length by reducing the diameter/width of the conductive portion 92. Therefore, the conductive portion 92 in the boundary region 78 may generate more heat per unit area to compensate for insufficient radiant heat from the adjacent conductive portion 90.

Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present disclosure can be implemented in a variety of forms. Therefore, while this disclosure has been described in connection with particular examples thereof, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims. 

1. A diesel particulate filter assembly comprising: a diesel particulate filter (DPF); and an electric heater that is integrally formed at an upstream end of the DPF, the electric heater including: a heating substrate that includes a central region and a boundary region around the central region; and a resistive heating element that includes a plurality of conductive portions, wherein adjacent ones of the conductive portions in the central region form a first spacing and adjacent ones of the conductive portions in the boundary region form a second spacing that is smaller than the first spacing.
 2. The diesel particulate filter assembly of claim 1 wherein a resistance of the plurality of conductive portions are constant per unit length of the resistive heating element.
 3. The diesel particulate filter assembly of claim 1 wherein the plurality of conductive portions have equal diameters.
 4. The diesel particulate filter assembly of claim 1 wherein the plurality of conductive portions have equal widths.
 5. The diesel particulate filter assembly of claim 1 wherein the plurality of conductive portions are connected in series.
 6. The diesel particulate filter assembly of claim 1 wherein the resistive heating element includes a heating wire embedded in the heating substrate.
 7. The diesel particulate filter assembly of claim 1 wherein the resistive heating element includes a resistive coating on a surface of the heating substrate.
 8. The diesel particulate filter assembly of claim 1 wherein the electric heater includes a mounting portion that surrounds the heating substrate and that secures the heating substrate to a wall of the DPF.
 9. The diesel particulate filter assembly of claim 1 wherein the heating substrate includes a porous ceramic substrate.
 10. The diesel particulate filter assembly of claim 1 wherein the conductive portions have a ring configuration.
 11. A diesel particulate filter assembly comprising: a DPF; and an electric heater that is provided at an upstream end of the DPF and that includes: a heating substrate that includes a central region and a boundary region around the central region; and a resistive heating element that is provided on the substrate and that includes a plurality of conductive portions, wherein the conductive portions in the boundary region have a resistance per unit length larger than that in the central region.
 12. The diesel particulate filter assembly of claim 11 wherein adjacent ones of the conductive portions in the central region have a first spacing and adjacent ones of the conductive portions in the boundary region have a second spacing, wherein the first spacing is equal to the second spacing.
 13. The diesel particulate filter assembly of claim 11 wherein adjacent ones of the conductive portions in the central region have a first spacing and adjacent ones of the conductive portions in the boundary region have a second spacing that is smaller than the first spacing.
 14. The diesel particulate filter assembly of claim 11 wherein at least one of the conductive portions in the boundary region has a diameter smaller than that of the conductive portions outside the boundary region.
 15. The diesel particulate filter assembly of claim 11 wherein at least one of the conductive portions in the boundary region has a width smaller than that of the conductive portions outside the boundary region.
 16. The diesel particulate filter assembly of claim 11 wherein the conductive portions are connected in series. 